Desiccation sensitivity and tolerance in the moss Physcomitrella patens: assessing limits and damage.

Authors: KOSTER, KAREN - University Of South Dakota; BALSAMO, RONALD - Villanova University; CATHERINE, ESPINOZA - University Of Missouri; Oliver, Melvin

Submitted to: Plant Growth Regulation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/2010
Publication Date: 6/18/2010
Citation: Koster, K.L., Balsamo, R.A., Catherine, E., Oliver, M.J. 2010. Desiccation sensitivity and tolerance in the moss Physcomitrella patens: assessing limits and damage. Plant Growth Regulation. 62:293-302.

Interpretive Summary: The moss Physcomitrella patens is rapidly becoming the model of choice for functional genomic studies of plant stress responses at the cellular level. It is a simple plant where the environment acts directly upon the cell, without the confounding aspects of complex tissues and plant architecture. In the study of plant dehydration it is of great importance because with the ability to test the efficacy of single genes in improving cellular dehydration tolerance has great impact on our studies on single gene candidates drought tolerance improvement. In this study we have used physical measurements to delineate the limits of dehydration tolerance for the wild type plant and to determine when and how much cellualr damage occurs at various precise water deficits. We have demonstrated that Physcomitrella patens is relatively dehydration tolerant, compared to crop plants, but is not tolerant of water loss that renders the plant stressed to <-13 MPa ( measure of water potential). Crop plants rarely tolerate water potentials of -4MPa. Treatment of Physcomitrella with the palnt hormone ABA rendered the plant tolerant of water deficits to -273 MPa, a level of dehydration that classifies a plant as desiccation tolerant. Light microscopy demonstrated cells were shrunken and their walls twisted, even at -13 MPa. and unless treated with ABA would exhibit extensive damage when rehydrated. These results have a major impact on our investigations into which genes improve cellular dehydration tolerance and will speed our ability to develop genetic strategies for the improvement of drought tolerance in crops.

Technical Abstract: The moss Physcomitrella patens is becoming the model of choice for functional genomic studies at the cellular level. Studies report that P. patens survives moderate osmotic and salt stress, and that desiccation tolerance can be induced by exogenous ABA. Our goal was to quantify the extent of dehydration tolerance in wild type moss and to examine the nature of cellular damage caused by desiccation. We exposed P. patens to humidities that generate plant water potentials from -4 (97% RH) to -273 MPa (13% RH) and monitored water loss until equilibrium. Water contents were measured on a dry matter basis to determine the extent of dehydration because fresh weights (FW) were found to be variable and, therefore, unreliable. We measured electrolyte leakage from rehydrating moss, assessed overall regrowth, and imaged cells to evaluate their response to drying and rehydration. Physcomitrella did not routinely survive water potentials <-13 MPa. Upon rehydration, moss dried to water contents > 0.4 g g dm-1 maintained levels of leakage similar to those of hydrated controls. Moss dried to lower water contents leaked extensively, suggesting that plasma membranes were damaged. Moss protonemal cells were shrunken and their walls twisted, even at -13 MPa. Moss cells rehydrated after drying to -273 MPa failed to re-expand completely, again indicating membrane damage. ABA treatment elicited tolerance of desiccation to at least -273 MPa and limited membrane damage. Results of this work will form the basis for ongoing studies on the functional genomics of desiccation tolerance at the cellular level.